santa.go

// サンタクロース問題
// http://karetta.jp/article/blog/oneline/030756
package main

import (
	"fmt"
	"math/rand"
	"reflect"
	"time"
)

var r *rand.Rand

type visitor interface {
	act(home chan visitor)
}

type elf struct {
	id int
}

type reindeer struct {
	id int
}

func (d elf) act(home chan visitor) {
	time.Sleep(time.Duration(r.Int63n(10)) * time.Second)
	fmt.Printf("Elf #%d came to Santa's home\n", d.id)
	home <- d
}

func (c reindeer) act(home chan visitor) {
	time.Sleep(time.Duration(r.Int63n(8)) * time.Second)
	fmt.Printf("Reindeer #%d came to Santa's home\n", c.id)
	home <- c
}

func startReindeers(home chan visitor) {
	for i := 0; i < 9; i++ {
		c := reindeer{i}
		go c.act(home)
	}
}
func startElfs(home chan visitor) {
	for i := 0; i < 10; i++ {
		d := elf{i}
		go d.act(home)
	}
}

func release(all []visitor, home chan visitor) []visitor {
	for _, member := range all {
		go member.act(home)
	}
	return queue()
}

func queue() []visitor {
	return make([]visitor, 0, 10)
}

func main() {
	r = rand.New(rand.NewSource(time.Now().Unix()))
	home := make(chan visitor)

	startReindeers(home)
	startElfs(home)

	reindeers := queue()
	elfs := queue()

	for i := 0; i < 50; i++ {
		visitor := <-home
		name := reflect.TypeOf(visitor).Name()

		if name == "reindeer" {
			reindeers = append(reindeers, visitor)
		} else if name == "elf" {
			elfs = append(elfs, visitor)
		}
		if len(reindeers) == 9 {
			fmt.Println("*** Santa went to deliver presents: ", reindeers)
			time.Sleep(time.Duration(10) * time.Second)
			reindeers = release(reindeers, home)
			fmt.Println("*** Delivery finished")
		}
		if len(elfs) == 3 {
			fmt.Println("### Santa is meeting up with elfs: ", elfs)
			time.Sleep(time.Duration(5) * time.Second)
			elfs = release(elfs, home)
			fmt.Println("### Meeting finished")
		}
	}
	fmt.Println("Finished.")
}